1. Field of the Invention
The present invention relates to a wire-electric discharge machine having a cutoff piece taking out mechanism for taking out a cutoff piece produced by wire-cut electric discharge machining.
2. Description of Related Art
In a wire-cut electric discharge machine for machining a workpiece by electric discharge generated between a wire electrode and the workpiece by applying electric voltage in-between, there has been arisen a problem how to automatically take out a cutoff piece, which is a product of the electric discharge machining or a waste to be removed, from the workpiece and there has been various proposals for such a problem.
As devices for holding a cutoff piece and taking out the cutoff piece upwardly, there have been proposed a device for attracting a cutoff piece by suction means (see for example JP 2826357B), a device for attracting a cutoff piece by magnet (permanent magnet or electric magnet, see for example JP 60-242195A, JP 7-67651B). Further, as a device for removing a cutoff piece to be dropped from the workpiece, there are known a device in which the dropped cutoff piece is received by a plate and transferred with the plate by an actuator (see for example JP 2566461B) and a device in which the dropped cutoff piece is received by a basket and transferred by a robot or an actuator (see for example JP 2002-263958A).
However, cutoff pieces produced by the wire-cut electric discharge machine, one of which is shown in FIG. 4 for example, have various and complicated shapes. In FIG. 4, a reference numeral 1 denotes a workpiece and a reference numeral 2 denotes a cutoff piece cut off from the workpiece by the wire-electric discharge machining. In the device as disclosed in JP 2002-263958A, it is necessary to hold at a center of gravity of the cutoff piece so as not to incline the cutoff piece of a complicated shape in taking out the cutoff piece upwardly, and thus means for calculating a position of the center of gravity of the cutoff piece. Further, even if the position of the center of gravity is calculated, since a suction pad is relatively small, there is a case where the holding position is slightly displaced from the center of gravity in sucking a large cutoff piece to incline the cutoff piece so that the cutoff piece is disable to be smoothly lifted up from the workpiece making interference with the workpiece.
In the device as disclosed in JP 7-67651B employing permanent magnets, it is necessary to fix permanent magnets (magnet holders) at a predetermined arrangement on a base plate by screws in accordance with a shape of a cutoff piece and thus has a difficulty in taking out cutoff pieces of various shapes automatically and efficiently.
In the device as disclosed in JP 60-242195A employing electromagnets, it is improved to take out cutoff pieces of various shapes automatically and efficiently by selecting appropriate electromagnets in accordance with a shape of cutoff piece to be taken out. However, as inherence of the electromagnets, magnetization of cores of the electromagnets is not released as being used for a long time and has a problem that it is difficult to attract the cutoff piece by magnetize the appropriate electromagnets only in accordance with a shape of a cutoff piece to be taken out.
Further, in the devices in which a cutoff piece is removed by being dropped from the workpiece as disclosed in JP 2566461B and JP 2002-263958A, a balance of the cutoff piece of complicated shape may be lost and the cutoff piece may make contact with the workpiece to fail in smoothly dropping from the workpiece or in dropping from the workpiece as being caught by the workpiece.